[throwawayapples]

Here's what it's focused on, targeting Themelio cryptocurrency's requirements:

> In a blockchain, the behavior we almost always want is for all transactions on the database to be serializable and for database integrity to be guaranteed — that is, a transaction either happens completely or not all, and crashes/power failures cannot cause inconsistency — but we do not need strong durability. We don’t need to ensure that a information saved to disk is still there if the system crashes immediately, since generally Themelio will tolerate “traveling back in time” a few seconds.

> The combination of extremely robust serializability and integrity with eventual durability is hard to find. SQLite in WAL mode with PRAGMA synchronous = NORMAL is close, but directly using SQLite still has relatively poor performance with the extremely fragmented reads and writes Themelio nodes create. LMDB and friends simply give no option besides either synchronizing every transaction or leaving database integrity up to chance every time a power failure might happen.

> ... We actively encourage use of BoringDB outside of Themelio; we think it’s the perfect choice whenever you need a single-process, embedded key-value database with extreme reliability but also reasonable write performance.

It's written in Rust with a permissive license.